Magnetic and magneto-optical media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A conventional, single-sided, longitudinal magnetic recording medium 1 in e.g., disk form, such as utilized in computer related applications, is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium, having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers typically include a plating layer 11, as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic recording layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (DLC), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound.
Magneto-optical (MO) recording media (MO) similarly comprise a laminate of layers formed over a suitable substrate, e.g., a disk. By way of illustration, shown in FIG. 2 is a single-sided MO medium 20 having a first surface magneto-optical (FSMO) layer configuration, wherein reference numeral 21 denotes a disk-shaped substrate formed of a material selected from, for example, aluminum (Al), plated aluminum, aluminum alloys, metals, metal alloys, glass, ceramics, and glass-ceramic composite materials. Formed on one surface 21A of substrate 21 is a layer stack, comprising, in sequence from surface 21A, a reflective, heat sinking layer 22, comprising Al or an alloy thereof, e.g., AlCr, AlTi, AlCu, AlMo, etc., which layer may also serve to prevent laser beam transmission through the substrate when the latter is transparent, as in the case of glass or glass-based materials, and thus render surface 21A opaque; a first dielectric material layer 23, substantially transparent to the wavelength(s) of the at least one laser beam employed for writing and reading out information stored in the medium, typically selected from SiN.sub.x, AlN.sub.x, SiO.sub.x, and AlO.sub.x ; a MO read-write layer 24, for example, comprising a rare earth-transition metal thermo-magnetic (RE-TM) material having perpendicular magnetic anisotropy, large perpendicular coercivity H.sub.c at room temperature, and high Curie temperature T.sub.c, typically selected from TbFe, TbFeCo, TbDyFeCo, etc.; a second transparent dielectric material 25 typically selected from the same materials utilized for the first transparent dielectric layer 23; a thin, amorphous, diamond-like carbon (DLC) protective overcoat layer 26; and a lubricant topcoat layer 27, typically comprising a fluoropolyether or perfluoropolyether material.
A promising new class of materials suitable for use as the magnetic recording layer 13 of the magnetic medium of FIG. 1 or the MO read-write layer 24 of the magneto-optical (MO) medium of FIG. 2 includes cobalt/platinum (Co/Pt).sub.n and cobalt-palladium (Co/Pd).sub.n multilayer stacks, also referred to as "superlattice" structures. As schematically illustrated in FIG. 3, such multilayer stacks or superlattice structures 30 comprise n pairs of alternating discrete layers of Co (designated by letter A in the drawing) and Pt or Pd (designated by letter B in the drawing), where n=an integer between about 10 and about 30. Superlattice 30 is typically formed by a suitable vapor deposition technique and can exhibit perpendicular magnetic anisotropy arising from metastable chemical modulation in the direction normal to the substrate. Compared to conventional cobalt-chromium (Co--Cr) alloys utilized in magnetic data storage/retrieval disk applications, such (Co/Pt).sub.n and (Co/Pd).sub.n multilayer or superlattice structures offer an economic advantage in facilitating room temperature deposition processing necessary for utilization of lower cost polymeric substrates. When utilized in MO disk-based applications, (Co/Pt).sub.n and (Co/Pd).sub.n superlattices offer superior corrosion resistance and blue wavelength response vis-a-vis conventional RE-TM alloys.
For example, a (Co/Pt).sub.n multilayer stack or superlattice 30 suitable for use as the magnetic recording layer 13 of the magnetic recording medium of FIG. 1 or the magneto-optical (MO) read-write layer 24 of the MO medium of FIG. 2 can comprise a plurality of Co/Pt pairs, i.e., n=about 10 to about 30, e.g., 13, wherein each Co/Pt pair consists of a 3 .ANG. thick Co layer adjacent to an 8 .ANG. thick Pt layer, for a total of 26 separate or discrete layers. When utilized as a high recording density magneto-optical (HDMO) read-write layer 24 in e.g., a MO medium as illustrated in FIG. 2, such multilayer stacks or superlattice structures 30 are characterized by having a large perpendicular anisotropy and high coercivity, high squareness ratio (S) for a magnetic hysteresis (M-H) loop measured in the perpendicular direction, and high Kerr rotation angle for light of a particular wavelength region, e.g., blue or red light. By way of illustration, but not limitation, (Co/Pt).sub.n and (Co/Pd).sub.n HDMO superlattices, wherein n=about 10 to about 30 pairs of Co and Pt or Pd layers having thicknesses as indicated supra and fabricated, e.g., by means of techniques disclosed in U.S. Pat. No. 5,750,270, the entire disclosure of which is incorporated herein by reference, exhibit perpendicular anisotropy exceeding about 2.times.10.sup.6 erg/cm.sup.3 ; coercivity as high as about 5,000 Oe; squareness ratio (S) of a M-H loop, measured in the perpendicular direction, of from about 0.85 to about 1.0; and carrier-to-noise ratio (CNR) of from about 30 dB to about 60 dB.
According to conventional methodologies and practices for automated manufacture of disk-shaped magnetic and MO media, when the various above-described thin film layers constituting the medium are deposited on the disk-shaped substrates, as by cathode sputtering techniques, it is generally advantageous to coat one disk at a time with the various requisite layers. However, the continuing requirement for increased storage density has increased the number of requisite layers and, as the number of requisite layers increases, it becomes impractical to build and operate multi-chamber cathode sputtering apparatus wherein each separate or discrete layer to be deposited requires a separate sputtering cathode/target assembly and associated vacuum chamber because either the system becomes unwieldy as a result of its great length in the case of linearly-arranged deposition systems, or in the case of circularly-configured systems, the diameter of the circle becomes too large.
The above-described difficulty associated with increasing numbers of requisite layers is magnified in the case of recording media comprising (Co/Pt).sub.n or (Co/Pd).sub.n multilayer stacks or superlattice structures where n=about 10 to about 30 layer pairs due to the very large number of individual layers required to be deposited. Currently available disk processing apparatus, whether pallet pass-by, single disk, or some variation thereof, do not have an adequate cathode count for single-pass coating of a large number of layers. Certain types of existing sputtering apparatus can be modified to perform multiple pass, back-and-forth, or up-and-down repetitive disk transport to fabricate multilayer stacks with a limited number of sputtering cathodes, but such reduction in cathode number incurs a significant reduction in productivity, hence increased manufacturing cost. Other types of existing sputtering apparatus, e.g., the Intevac MDP style frequently utilized for magnetic and MO recording disk manufacture, transport each disk with an intermittent up-and-down motion which can be exploited for reducing the requisite number of coating stations; however, the required number of sputtering cathode/target assemblies cannot be reduced.
It is considered that a method and apparatus for forming multilayer stacks or superlattice structures which minimizes the requisite number of sputtering cathode/target assemblies without sacrificing productivity is required for realizing economically viable manufacture of (Co/Pt).sub.n and (Co/Pd).sub.n superlattice-based magnetic and/or MO recording media. One possible approach for achieving such result is to utilize nested, annularly-shaped, independently powered Co and Pt or Pd sputtering cathodes/targets which can be alternately energized to sputter discrete layers of Co and Pt or Pd to form a multilayer stack. However, this approach entails several drawbacks, e.g., fabrication of the annularly-shaped targets is expensive, the cathode/target structure is mechanically complex, and there is limited control of the film thickness and properties in the radial direction.
Another approach involves providing an array of sputtering cathodes/targets and rotating the substrate pallet or individual disk in facing relation to the cathode/target array. However, this approach raises concerns of machine reliability and cleanliness resulting from the additional motion of coated parts and mechanical linkages in the vacuum system, particularly in the case of manufacture of dual-sided media.
Accordingly, there exists a need for improved means and methodology for forming, as by cathode sputtering, multilayer stacks or superlattice structures, for use in e.g., single- and dual-sided magnetic and/or MO data/information storage and retrieval media in disk form, which means and methodology form part of a multi-station processing apparatus and enable rapid, simple, and cost-effective formation of such media by forming multilayer stacks or superlattice structures via sputtering utilizing a single, rotating multiple-cathode/target assembly and a stationary substrate.
The present invention, wherein multilayer or superlattice structures are formed according to a different approach utilizing a single, rotating multiple magnetron cathode/target assembly and a stationary substrate, effectively addresses and solves problems attendant upon the use of sputtering techniques for the manufacture of, inter alia, high recording density, thin film magnetic and MO media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology. Further, the means and methodology provided by the present invention enjoy diverse utility in the manufacture of other devices and products requiring multilayer thin film coatings.